Fluid flow plate for a fuel cell

ABSTRACT

A fluid flow plate for an electrochemical assembly has a plurality of first fluid flow channels extending across an active area of the flow plate to define a first fluid flow field of the fluid flow plate and a plurality of second fluid flow channels extending across the active area of the flow plate to define a second fluid flow field of the fluid flow plate. An array of first fluid transfer points is disposed along an edge of the first fluid flow field for communicating fluid into or out of the first fluid flow channels. An array of second fluid transfer points is disposed along an edge of the second fluid flow field for communicating fluid into or out of the second fluid flow channels. A first fluid gallery a first peripheral edge portion bounded by the array of first fluid transfer points and has a second peripheral edge portion forming a first fluid communication edge of the fluid flow plate. A second fluid gallery has a first peripheral edge portion bounded by the array of second fluid transfer points and has a second peripheral edge portion forming a second fluid communication edge of the fluid flow plate. The first fluid gallery and the second fluid gallery are shaped such that the combined lengths of the second peripheral edge portions are longer than the first peripheral edge portion of the second fluid gallery or the first fluid gallery. Increasing the lengths of the second peripheral edge portions of each gallery to the maximum possible length compared to the length of fluid transfer points (i.e. width of the active flow field area) optimises fluid distribution into the channels of the flow plate.

The invention relates to fluid flow plates for electrochemical fuel cellassemblies, and in particular to configurations of bipolar or monopolarplates allowing for multiple fluid flow channels for the passage of twoor more of anode, cathode and coolant fluids.

The use of bipolar, as opposed to unipolar, plates in electrochemicalfuel cells allows for a reduction in thickness and consequently overallsize of the fuel cell, due to the use of shared electrical connectionsbetween the anode plate of one cell and the cathode plate of an adjacentcell. Conventional bipolar plates may for example be formed from asingle sheet of metal, with machined or pressed features on opposingfaces to allow for the passage of fuel and oxidant.

In so-called ‘open cathode’ fuel cell assemblies, cathode fluid flowchannels allow for free passage of air through the fuel cell assembly,which functions both to supply oxidant to the individual cells and toprovide cooling. A problem with such arrangements is that the fuel cellassembly needs large amounts of forced air to achieve both functions,and the cathode channels therefore need to be large to accommodatesufficient air flow. Reducing the size of such assemblies can bedifficult, as the efficiency of cooling by such means can be compromisedby making the cathode channels smaller.

The use of so-called ‘closed cathode’ fuel cell assemblies addresses theproblem of forced air cooling by instead using dedicated coolantchannels provided within the bipolar plate, while the cathode channelsfunction mainly to provide oxidant. Such coolant channels may beprovided by mating a pair of pre-machined plates together to providechannels running between the plates. This arrangement allows for coolantfluid, typically water, to be passed through a bipolar plate when inuse, which greatly increases the efficiency of cooling compared toforced air cooling in open cathode assemblies.

A problem with such closed cathode assemblies, however, is that thecomplexity of each individual cell is increased due to the need foradditional coolant channels. This can result in an increase, rather thana decrease, in the overall size of each cell. This also results in anincreased cost for manufacturing each cell.

Other problems to be addressed in fuel cell assemblies include: ensuringa uniform flow field for fluid distribution in fuel, oxidant and coolantlines; minimising the pressure drop across inlet manifolds; minimisingthe sealing pressure required to ensure gas-tight operation; making theconstruction of a bipolar plate compatible with mechanised assemblyprocesses, given the large number of units that need to be assembledwith precision in manufacturing a fuel cell assembly; reducing the pitchof the fuel cells making up a stack while maintaining operation withindesired parameters; reducing the number of components; reducing theoverall weight; reducing material usage and wastage; simplifying thedesign, manufacture and assembly; and in general reducing the overallcost of a fuel cell assembly.

It is an object of the invention to address one or more of the abovementioned problems.

According to one aspect, the present invention provides a fluid flowplate for an electrochemical assembly, comprising:

-   -   a plurality of first fluid flow channels extending across an        active area of the flow plate to define a first fluid flow field        of the fluid flow plate;    -   a plurality of second fluid flow channels extending across the        active area of the flow plate to define a second fluid flow        field of the fluid flow plate;    -   an array of first fluid transfer points disposed along an edge        of the first fluid flow field for communicating fluid into or        out of the first fluid flow channels;    -   an array of second fluid transfer points disposed along an edge        of the second fluid flow field for communicating fluid into or        out of the second fluid flow channels;    -   a first fluid gallery having a first peripheral edge portion        bounded by the array of first fluid transfer points and having a        second peripheral edge portion forming a first fluid        communication edge of the fluid flow plate,    -   a second fluid gallery having a first peripheral edge portion        bounded by the array of second fluid transfer points and having        a second peripheral edge portion forming a second fluid        communication edge of the fluid flow plate,    -   wherein the first fluid gallery and the second fluid gallery are        shaped such that the combined lengths of the second peripheral        edge portions are longer than the first peripheral edge portion        of the second fluid gallery or the first fluid gallery.

The fluid communication edges of the fluid flow plate may compriseinternal edges of the flow plate. The fluid communication edges of thefluid flow plate may comprise both internal and external edges of theflow plate. The internal edges of the flow plate may form at least partof at least one port passing through the flow plate. The communicationedges may each comprise a castellated structure. The second peripheraledge portion of the second fluid gallery may comprises at least one edgedisposed at an oblique angle to the first peripheral edge portion of thesecond fluid gallery. The second peripheral edge portion of the firstfluid gallery may comprise at least one edge disposed at an obliqueangle to the first peripheral edge portion of the first fluid gallery.At least one of the first fluid gallery and the second fluid gallery mayhave a portion with a generally triangular configuration, the firstperipheral edge portion forming at least part of a base of thetriangular configuration and the second peripheral edge portion forminga side of the triangular configuration. The first fluid gallery and thesecond fluid gallery may at least partially overlap one another. Thefirst peripheral edge portion of the first fluid gallery and the firstperipheral edge portion of the second fluid gallery may be superposed onone another. The second fluid gallery may be shaped such that the secondperipheral edge portion is longer than the first peripheral edgeportion. The second fluid gallery may be shaped such that the secondperipheral edge portion is at least 1.2 times longer, or preferably atleast 1.5 times longer, than the first peripheral edge portion.

The fluid flow plate may further include:

-   -   a plurality of third fluid flow channels extending across the        active area of the fluid flow plate to define a third fluid flow        field of the fluid flow plate;    -   an array of third fluid transfer points disposed along an edge        of the third fluid flow field for communicating fluid into or        out of the third fluid flow channels;    -   a third fluid gallery having a first peripheral edge portion        bounded by the array of third fluid transfer points and having a        second peripheral edge portion forming a third fluid        communication edge of the fluid flow plate,    -   wherein the third fluid gallery is shaped such that the length        of the second peripheral edge portion of the third fluid gallery        is at least as long as the first peripheral edge portion of the        third fluid gallery.

The first fluid gallery, the second fluid gallery and the third fluidgallery may all be shaped such that the combined length of the secondperipheral edge portions thereof is at least two times longer, orpreferably at least three times longer, than the first peripheral edgeportion of the first fluid gallery or the second fluid gallery or thethird fluid gallery.

Aspects and embodiments of the invention are described in further detailbelow by way of example and with reference to the enclosed drawings inwhich:

FIG. 1 is a perspective view of a bipolar plate separated to showinternal coolant manifold and fluid flow channels, and external cathodemanifold and fluid flow channels;

FIG. 2 is a perspective view of the reverse face of the bipolar plate ofFIG. 1, showing anode manifold and fluid flow channels;

FIG. 3 is a magnified view of the coolant and cathode manifolds and flowchannels of the bipolar plate of FIG. 1;

FIG. 4 is a magnified view of the anode manifold and fluid flow channelsof the bipolar plate of FIG. 2;

FIG. 5 is a detailed view of a coolant port manifold in one of thecorrugated plates making up a bipolar plate;

FIG. 6 is a detailed view of the underlying corrugated plate in thedetailed view of FIG. 5;

FIG. 7 is a sectional view transverse the fluid flow field region of abipolar plate, showing the arrangement of interengaging corrugations inthe first and second corrugated plates making up the anode, cathode andcoolant fluid flow channels;

FIG. 8 is a sectional view of a cathode port and manifold connecting toa series of cathode fluid flow channels;

FIG. 9 is a sectional view of an anode manifold connecting to a seriesof anode fluid flow channels;

FIG. 10 is a sectional view through a cathode port and cathode manifold;

FIG. 11 a is a perspective view of an anode side of a bipolar plate;

FIG. 11 b is a perspective view of a cathode side of the bipolar plateof FIG. 11 a;

FIG. 12 a is a detailed sectional view of a transverse fluid connectionregion in an assembled bipolar plate;

FIG. 12 b is an alternative detailed sectional view of a transversefluid connection region in an assembled bipolar plate;

FIG. 13 is a sectional view through a corrugated region and an anodemanifold region of a bipolar plate;

FIG. 14 is an illustration of anode, cathode and coolant fluid volumeswithin a bipolar plate;

FIG. 15 is a sectional view of the fluid volumes of FIG. 14;

FIG. 16 is a sectional view of a stack comprising five membraneelectrode assemblies and six bipolar plates;

FIG. 17 is a partial perspective view of a cathode face of analternative embodiment of bipolar plate;

FIG. 18 is a partial perspective view of an anode face of the bipolarplate of FIG. 17;

FIG. 19 is a partial perspective view of a coolant manifold on a reverseof the anode face of the bipolar plate of FIGS. 17 and 18; and

FIG. 20 is a perspective view of a multi-plate assembly of the bipolarplates of FIGS. 17-19.

FIGS. 1 to 10 illustrate a first type of bipolar plate, in which ananode fluid flow field across a face of the plate is in the form of anarrangement of parallel tracks or channels. FIGS. 11 to 15 illustrate asecond type of bipolar plate, in which the anode fluid flow field is inthe form of a single serpentine track or channel across the face of theplate. These different embodiments require different arrangements ofchannels in the bipolar plate, as described in further detail below.

FIGS. 1 and 2 show perspective views of an embodiment of a bipolar plate10. The bipolar plate 10 comprises first and second corrugated plates11, 12 that engage together to form the assembled bipolar plate 10. Thefirst plate 11 comprises a first plurality of fluid flow channels 13across a first face of the bipolar plate 10, in the form of corrugationsextending between first inlet and outlet ports 18 a, 18 b at opposingends of the bipolar plate. In the arrangement shown, these ports 18 a,18 b are used for the flow of cathode fluid, i.e. oxidant, through theassembled fuel cell formed from a stack of such plates. The firstplurality of fluid flow channels 13 formed by the corrugations may bealternatively described as cathode fluid flow channels. A cathodemanifold or gallery 15 a, 15 b is provided at each end of the plate 10connecting the respective ports 18 a, 18 b and the fluid flow channels13. The manifolds or galleries 15 a, 15 b serve to distribute fluidflowing into and out of the stack through the ports 18 a, 18 b among thefluid flow channels 13 with a minimum pressure differential across thewidth of the plate 10, so as to achieve a uniform flow of fluid alongthe channels 13.

Second inlet and outlet ports 19 a, 19 b are provided at opposing endsof the bipolar plate 10 for flow of fluid into and out of the plate andalong a second plurality of fluid flow channels 22 provided on a secondopposing face of the bipolar plate 10, as shown in the reverse view ofthe plate in FIG. 2. These second fluid flow channels 22 may bedescribed as anode fluid flow channels, and the ports 19 a, 19 b asanode ports, for the distribution of fuel gas through and across thebipolar plate 10. Anode manifold regions or galleries 21 a, 21 b areprovided connecting the anode inlet and outlet ports 19 a, 19 b to thesecond plurality of fluid flow channels 22.

Third inlet and outlet ports 17 a, 17 b are also provided in the plate10 for the transmission of coolant fluid, such as water, into and out ofthe bipolar plate 10 when assembled into a fuel cell stack. These ports17 a, 17 b communicate, via coolant manifolds or galleries (only gallery16 b is visible), with a third plurality of fluid flow channels 14extending between the third inlet and outlet ports 17 a, 17 b atopposing ends of the bipolar plate 10. The third plurality of fluid flowchannels 14 are provided between the first and second corrugated plates11, 12 forming the first and second opposing faces of the bipolar plate10. In the embodiment illustrated in FIGS. 1 and 2, corrugations makingup the third plurality of fluid flow channels 14, i.e. the coolantchannels, are provided by engagement of the reverse sides of thecorrugations in the plates 11, 12 making up the first and secondplurality of fluid flow channels. This is illustrated in further detailin FIG. 7, described below.

The form of the bipolar plate 10 may be fabricated from a singlepress-formed corrugated metal plate comprising the first (or cathode)plate 11 and the second (or anode) plate 12, which may be connected viaa fold line. The plates 11, 12 can then be folded together along theadjoining fold line to interleave the corrugations forming the third setof fluid flow channels between the plates 11, 12. The press-formingprocess can also form the ports 17 a, 17 b, 18 a, 18 b, 19 a, 19 b inthe same step as forming the fluid flow channels 13, 14, 22.

Applied to faces of each of the corrugated plates 11, 12 making up thebipolar plate 10 are gaskets 23 a, 23 b, 23 c, which act to providefluid seals around the periphery of the opposing outer faces of thebipolar plate 10 and between the first and second corrugated plates 11,12. The gaskets 23 a, 23 b, 23 c are preferably provided in the form ofmoulded elastomeric material applied to the faces of the corrugatedplates 11, 12. As well as providing fluid seals around the periphery ofthe plate 10, and around the periphery of each of the inlets andoutlets, the moulded gasket material provides additional surface detailto form the inlet and outlet manifolds for each of the fluid flowchannels 13, 14, 22, as shown in further detail in subsequent figures.The patterns in the moulded gaskets 23 a, 23 b, 23 c allow forconduction of air, fuel (hydrogen) and coolant (water) to be directedfrom inlet ports to the relevant channels formed in and between theplates 11, 12 and from these channels to exhaust ports. The plates 11,12 illustrated in FIG. 1 and subsequent figures are symmetrical, so theports 17 a, 18 a, 19 a or 17 b, 18 b, 19 b can be considered eitherinlet or outlet ports. Flow of fluid from each inlet port to thecorresponding outlet port can be in a common direction or in differentdirections, depending on the particular implementation.

The anode and cathode manifolds 21 a, 21 b, 15 a, 15 b are each shapedto minimise the pressure drop across the width of the flow fields.

FIG. 3 illustrates a magnified view of one end of the bipolar plate 10of FIG. 1, showing the cathode manifold or gallery 15 b and the coolantmanifold or gallery 16 b. The cathode manifold 15 b comprises an openarray of raised features formed in the gasket material, the raisedfeatures being configured to provide a defined separation between thebipolar plate and an adjacent layer (which in this case is themembrane-electrode assembly, or MEA) while allowing a flow of fluidbetween the cathode port 18 b and the fluid flow field 13 formed bycorrugations in the first plate 11. In the embodiment shown, acastellated region 31 of the cathode manifold 15 b is disposed along anedge of the manifold region 15 b adjoining the port 18 b, thecastellated region 31 serving to direct the flow of fluid into or out ofthe manifold 15 b while maintaining a required separation along the edgeof the manifold region 15 b. In the space between the castellated regionand the cathode fluid flow field 13, the manifold 16 b comprises anarray of projections 33 in the gasket material configured to allow freeflow of fluid into or out of the corrugations 13.

A similar arrangement of raised features in the gasket material isprovided for the coolant manifold 16 b and for the anode manifold 21 b,as illustrated in FIG. 4. Each of the manifolds 15 b, 16 b, 21 b isprovided with a castellated region 31, 32, 34 adjacent the correspondingport 18 b, 17 b, 19 b and with arrays of projections in the mouldedgasket between the port 17 b, 19 b and the fluid flow field 22, 14. Eachof the manifolds is shaped to minimise a pressure difference across thecorresponding flow field and to maximise the inlet and outlet area. Thecombination of generally triangular shaped ports with shaped manifoldsallows for an optimum use of area at each end of the generallyrectangular bipolar plate.

Illustrated in FIG. 5 is a more detailed perspective view of a region ofthe second plate 12 around the coolant port 17 b, showing thecastellated region 32 in the manifold region along the edge of the port17 b between the port 17 b and the coolant fluid flow field 14. Thecorrugated plate 12 comprises a central metallic plate 51 having amoulded gasket 23 a, 23 c applied on opposing faces. The moulded gasket23 a on one face of the metallic plate 51 comprises the manifold 16 bwith the castellated region 32 along an edge adjoining the port 17 b.The gasket material is thicker over the castellated region 32 of themanifold 16 b compared with the periphery of the plate 12, to allow fora larger cross-sectional area for fluid to enter or exit the manifold.This is made possible by offsetting the metallic plate 51 under thecastellated region 32. This is illustrated more clearly in FIG. 6, whichshows the metallic plate 51 without the gasket layers 23 a, 23 capplied. An offset is provided in the plate 51 by means of a debossedregion 61 extending across an edge of the coolant port 17 b. A similararrangement may be applied in relation to the cathode and anode portsand manifolds.

FIG. 7 illustrates a transverse sectional view across the bipolar plate11, indicating the arrangement of corrugations allowing for fluid flowchannels across the anode, cathode and coolant fluid flow fields to becoplanar. Anode fluid flow channels 72 are provided by corrugations inthe second corrugated plate 12, comprising the metallic plate 51 andgasket layers 23 b, 23 c. Cathode fluid flow channels 73 are provided bycorrugations in the first corrugated plate 11, comprising metallic plate71 and the gasket layer 23 a. The gasket layer 23 b may instead beapplied to the first corrugated plate 11 to achieve the same result.

Coolant channels 74 are provided by openings in the space between themetallic plates 71, 51 of the first and second corrugated plates 11, 12.In the embodiment illustrated, the coolant channels 74 are formedbetween the first and second corrugated plates 11, 12 by omission ofselected corrugations in the second plate 12. The same effect may beachieved by omission of selected corrugations in the first plate 11. Thecoolant channels are preferably uniformly distributed across the widthof the bipolar plate 10, and provided by omission of alternatecorrugations in the second plate 12. In alternative arrangements, thecoolant channels may be formed between the first and second corrugatedplates by narrowing or by a height reduction of selected corrugations inthe first or second plate.

The arrangement of coolant channels in the bipolar plate allows for anefficient use of both space and material, since the corrugationsproviding fluid flow channels in the anode and cathode sides of theplate also serve to define a further set of fluid flow channels forcoolant between the corrugated plates.

The channels 72, 73, 74 on and between the corrugated plates 51, 71 areshown in FIG. 7 as being parallel to each other and substantiallyuniform along the length of the bipolar plate 10. In alternativeembodiments, the channels may be non-parallel and may for example betapered or varied in dimensions to account for expected pressure ortemperature variations across the bipolar plate 10 in use.

FIG. 8 shows a detailed sectional view of the bipolar plate,illustrating features of the cathode port 18 b and cathode manifold 15b. As for the coolant manifold, illustrated in FIG. 5 and describedabove, the cathode manifold 15 b comprises a castellated region 31formed in the gasket 23 a along an edge of the manifold 15 b adjoiningthe cathode port 18 b. Cathode fluid (i.e. oxidant and water) enteringor exiting the cathode fluid flow field formed by corrugations 13 isdirected to or from the port 18 b through the castellated region 31,which functions to maintain a separation between the underlying metallicplate 51 and an MEA against which the first face of the bipolar plate isin contact when assembled into a fuel cell stack.

FIG. 9 illustrates a detailed sectional view through the anode manifoldregion 21 b, in which a section of the castellated region 31 of thecathode manifold can also be seen.

The anode manifold region 21 b is typically of smaller thickness thanthe cathode manifold region 15 b, since a greater flow of fluid isrequired through the cathode fluid flow field than through the anodefluid flow field.

FIG. 10 illustrates a further sectional view through the cathodemanifold region 15 b, in which the coolant manifold 16 b can be seensandwiched between the metallic plates 51, 71. The debossed region 61corresponding to the castellated region 32, described above in relationto FIGS. 5 and 6, can also be seen in this view.

In the above described embodiment, the anode fluid flow field isprovided in the form of a plurality of parallel channels formed bycorrugations in the first corrugated plate 11. In alternativeembodiments the anode fluid flow field in the first corrugated plate maybe provided in the form of a serpentine track extending across the firstface of the bipolar plate. FIGS. 11 a and 11 b illustrates such anembodiment, where the bipolar plate 111 comprises a first face (FIG. 11a) having an anode fluid flow field 122 in the form of a singleserpentine track extending between anode inlet and outlet ports 119 a,119 b and a second face (FIG. 11 b) having a cathode fluid flow field113 in the form of an array of interdigitated corrugations extendingbetween cathode inlet and outlet ports 118 a, 118 b. The maindifferences as compared with the embodiment illustrated in FIGS. 1 to 10are the inclusion of transverse connecting regions 126 provided atopposing ends of the plate, forming fluid connections between adjacentanode fluid flow channels to allow the anode fluid flow channels totogether form a single track between the anode inlet and outlet ports119 a, 119 b.

The transverse connecting regions 126 are illustrated in more detail inFIGS. 12 a and 12 b, which respectively illustrate detailed sectionalviews of the second and first faces of the bipolar plate 111 through onesuch transverse connecting region. A return path is provided by eachtransverse connecting region 126 to connect adjacent anode fluid flowchannels 122. To allow for coolant to pass between the plates 171, 151between the coolant manifold 16 and each coolant channel 128, eachtransverse connecting region 126 has a depth that is less than the depthof the adjacent anode channels. Coolant can then pass beneath eachtransverse connecting region 126 and along the coolant channels 128. Tosupport the connecting regions, a plinth 125 is provided on the cathodefluid flow field, and a point of connection 127 is provided between themetallic plates 151, 171. The point of connection 127 may be a spot weldbetween the plates 151, 171, serving to maintain the relative positionof the plates and transmit pressure through the thickness of the plates151, 171 without collapsing the return path 126 or the coolant flowfield 128 provided between the plates. Each plinth 125 acts as a barrierbetween a longitudinally adjacent cathode fluid flow channel 113 b andan adjacent cathode manifold region 115 a, thereby separating thecathode flow channels into inlet channels 113 a (connected to thecathode manifold 115 a) and exhaust channels 113 b (connected to thecathode manifold 115 b) and forming the cathode fluid flow field 113into an array of interdigitated channels. Fluid passing from the cathodeinlet port 118 a passes across the cathode manifold 115 a and into theinlet channels 113 a. Fluid then passes along the inlet channels 113 aand diffuses through the gas diffusion layer (not shown) and into theoutlet channels 113 b. Fluid then passes along the cathode outletchannels 113 b and along the outlet channels 113 b into the outletmanifold 115 b and out of the plate 111 through the cathode outlet port118 b.

In a general aspect therefore, the second face of the bipolar plate maycomprise a fluid flow field 113 in the form of an array ofinterdigitated fluid flow channels 113 a, 113 b formed by corrugationsin the second face of the bipolar plate 111. Barriers 125 may beprovided at opposing ends of the interdigitated fluid flow channels,each barrier 125 configured to form a fluid seal between an adjacentlongitudinal fluid flow channel 113 a, 113 b and an adjacent inlet oroutlet manifold 115 b, 115 a.

FIG. 13 illustrates a cutaway perspective view of a section of thebipolar plate 111, in which the transverse connecting regions 126 areshown connecting adjacent pairs of anode channels 122. Coolant channels174 can also be seen extending longitudinally between the corrugatedplates 151, 171. Each coolant channel 174 extends along the bipolarplate 111 between a pair of adjacent anode channels 122 and connects tothe coolant manifold 16 via a gap between the plates 151, 171 beneath atransverse connecting region 126.

FIG. 14 illustrates a perspective view of the spaces between the platesmaking up the bipolar plate 111 of FIG. 11, corresponding to a coolantvolume 141, a cathode volume 142 and an anode volume 143. A moredetailed view of a portion of these volumes is provided in FIG. 15,illustrating sections taken parallel and transverse to the corrugationsin the plate. These exemplary views illustrate a general principleaccording to an aspect of the invention of transferring fluids from thevarious ports 141, 142, 143 with a minimal pressure drop and with auniform distribution to each of the fluid flow fields across the bipolarplate. This is achieved by maximising the length of the inlet of eachmanifold region and by overlapping the manifold regions through theplate. The use of an open array of raised features (described above inrelation to FIGS. 3 and 4) allows for the manifold regions to beoverlapping while maintaining a separation between adjacent plates toallow for fluid flow in an assembled fuel cell stack. This aspect willbe described in detail later.

FIG. 16 illustrates a sectional view through a fuel cell stack 160comprising five MEA layers and six bipolar plates 111 of the typeillustrated in FIG. 11. In each bipolar plate 111 a cathode plate 151 isbonded to an adjacent anode plate 171 by means of a spot weld 127connecting the plinth or barrier 125 in the cathode plate 151 with thecorresponding transverse connecting region 126 in the anode plate(described above in relation to FIGS. 12 a, 12 b). Anode and cathodeplates in adjacent bipolar plates are separated by a membrane electrodeassembly (MEA) 162 having a cathode gas diffusion layer 163 on one faceand an anode gas diffusion layer 164 on the other face. The MEA 162extends beyond the extent of the gas diffusion layers 163, 164, the MEAoverlaying the cathode manifold, 115, anode manifold 121 and the coolantmanifold 116 between the anode and cathode plates 151, 171. The cathodeport 118 is indicated in FIG. 16, connected to the cathode manifold 115via a castellated region 131 in each bipolar plate making up the stack160.

FIGS. 17, 18 and 19 illustrate a further alternative embodiment of abipolar plate 210. FIG. 17 shows the cathode face of the plate 210, FIG.18 the anode face and FIG. 19 the reverse of the anode face indicatingthe coolant manifold and channels. In this embodiment, the cathode ports218 are provided by an external enclosure (not shown), which provides anair flow through a pair of cathode air inlets to or from a cathodemanifold region 215, the cathode air inlets being provided on an outerperiphery or external edge 311 of the bipolar plate 210. As with theembodiments described above, the bipolar plate 210 comprises an anodeport 219 in fluid communication with an anode manifold region 221 (shownin FIG. 18), and a coolant port 217 in fluid communication with acoolant manifold region 216 (shown in FIG. 19). The anode, cathode andcoolant fluid flow regions across the plate 210 are otherwise similar tothe embodiment described above in relation to FIGS. 11 to 16. In thisembodiment, the cathode air inlet (or outlet) is configured to besubstantially larger in cross-sectional area than either of the coolantor anode inlets or outlets, thereby allowing a greater volume flow rateof air through the plate 210 in use. The anode inlet or outlet, which isdefined by the size of the anode port 219, is substantially smaller thaneither of the cathode or coolant inlets, since the volume of fluidpassing in or out of the anode port is smaller.

In a general aspect, according to the embodiment illustrated in FIGS.17-19 the second inlet and outlet ports 218 are provided on a peripheraledge of the bipolar plate 210, whereas the first and third inlet andoutlet ports 219, 217 are provided through the thickness of the bipolarplate 210. An advantage of this arrangement is that the second (cathode)inlet and outlet ports can be made substantially larger, allowing agreater flow of oxidant fluid into and out of the fuel cell made up of astack of such bipolar plates.

In this embodiment, unlike the embodiments described above in relationto FIGS. 1 to 16 where the manifold regions are partially overlapping,the manifold regions 215, 216, 221 of the plate 210 in FIGS. 17-19 areentirely overlapping due to the cathode port being provided on theperiphery of the plate, thereby allowing for a more uniform pressuredistribution across the width of the fluid flow regions of the plate210. The overlapping manifold regions also allows for a more uniformseal to be made around the peripheral edges of each of the manifoldregions.

An important feature of embodiments described above is the ability toprovide substantially increased lengths of fluid communication edge ofthe bipolar fluid flow plate.

Firstly, each of the cathode galleries or manifolds 15 a, 15 b (FIG. 1),115 a, 115 b (FIG. 11 b), 215 (FIG. 17) can provide fluid communicationand distribution between a cathode fluid port 18 a, 18 b, 118 a, 118 b,218 disposed at an end of the flow plate and a set of cathode fluid flowchannels 13, across a substantially full width of the flow field activearea of the plate defined by those channels.

Secondly, and correspondingly, each of the anode galleries or manifolds21 a, 21 b (FIG. 2), 121 a, 121 b (FIG. 11 a), 221 (FIG. 18) can providefluid communication and distribution between an anode port 19 a, 19 b,119 a, 119 b, 219 disposed at an end of the flow plate and a set ofanode fluid flow channels 22, across a substantially full width of theflow field active area of the plate.

Thirdly, and correspondingly, each of the coolant galleries or manifolds16 b (FIGS. 1 and 3), 216 (FIG. 19) can provide fluid communication anddistribution between a respective port 17 a, 17 b, 117 a, 117 b, 217disposed at an end of the flow plate and a set of coolant flow channels14, across a substantially full width of the flow field active area ofthe plate.

Each of the galleries (e.g. 15, 21, 16) has a first peripheral edgeportion bounded by an array of fluid transfer points disposed along anedge of the flow field defined by the flow channels 13, 14, 22. Thesefluid transfer points are exemplified by the channel ends indicated at301, 302, 303 respectively for cathode fluid transfer points, coolantfluid transfer points and anode fluid transfer points. Each of thegalleries (e.g. 15, 21, 16) also has a second peripheral edge portiondisposed along an edge of the flow plate, described herein as a fluidcommunication edge 320, 321, 322. The fluid communication edge providesfor delivery of fluid into the gallery (or egress of fluid from thegallery) by way of the plate edge that forms part of a side wall of therespective port, e.g. cathode fluid ports 18, 18 b, 118 a, 118 b, 218;anode fluid ports 19 a, 19 b, 119 a, 119 b, 219; and coolant fluid ports17 a, 17 b, 117 a, 117 b, 217. These fluid communication edges 320, 321,322 are exemplified by the castellated regions 31, 32, 34, 131, 132,134.

The first peripheral edge portions of each gallery are generallysuperposed on one another because the cathode flow channels 13, coolantflow channels 14 and anode flow channels 22 all generally definesubstantially the same active area, or flow field, of the bipolar plate10. However, the second peripheral edge portions (e.g. castellatedregions 31, 32, 34, 131, 132, 134) may not be superposed on one anotheras this would conflict with the requirement that the fluid communicationedges define parts of the side walls of separate fluid delivery portsextending through the planes of the bipolar plates in the fuel cellstack. For optimal distribution of fluids into the bipolar plate, it isbeneficial to have the maximum possible length of second peripheral edgeportions 31, 32, 34, 131, 132, 134 for each gallery 15, 21, 16. Thus,there exists a challenge to increase the total length of fluidcommunication edge of the bipolar plate for any given length of fluidtransfer points (i.e. width of the active flow field area).

Each of the embodiments described above achieves a degree of extensionof the total length of fluid communication edges 320, 321, 322 (secondperipheral edge portions of the galleries) compared with the length ofthe fluid transfer points (corresponding to the lengths of any of thefirst peripheral edge portions of the cathode gallery 15, anode gallery21 or coolant gallery 16).

In the arrangement of FIGS. 1 to 4, it can be seen that the triangularconfigurations of cathode ports 18, anode ports 19 and coolant ports 17and their relative positions, together with the corresponding generallytriangular shaping of the respective cathode galleries 15, anodegalleries 21 and coolant galleries 16 achieves a combined length ofsecond peripheral edge portions 31, 32, 34 that is greater than thelength of the first peripheral edge portion (i.e. the active area orflow field width) of any one of the cathode, anode or coolant galleries.In fact, the design sufficiently extends the lengths of the fluidcommunication edges that the combined length of second peripheral edgeportions 31, 32 for the cathode and coolant flows is greater than thelength of the first peripheral edge portion of any of the cathodegallery 15, anode gallery 21 or coolant gallery 16.

In the arrangement of FIGS. 11 a and 11 b, it can be seen that the ports117, 118, 119 are extended to provide greater volume, but each includesat least one edge portion (e.g. castellated region 131, 132, 134) whichis oblique to the first peripheral edge portion (e.g. at fluid transferpoints 301, 302, 303), thereby providing each of the galleries 115, 121,116 with at least one portion which is generally triangular in shape. Inthese galleries, the first peripheral edge portion may form the base ofa triangle, while the second peripheral edge portion may form a side ofthe triangle. Other more complex shapes are possible.

It will also be noted from FIG. 11 a that if the anode flow field 122 isprovided as a single serpentine channel extending from a single channelopening at each end of the plate, there will only be a single fluidtransfer point 303 and no need to extend the anode gallery 121 acrossthe full flow field 122 width and it may not be necessary to have ananode gallery. However, the principles described with respect to ananode gallery 121 having a first peripheral edge portion extendingacross the width of the anode flow field can still apply where multipleserpentine channels are provided.

In a general aspect, the total length of fluid communication edges 320,321, 322 can be achieved by presenting at least one, and preferably morethan one, of the second peripheral edge portions of one or more of thegalleries 15, 21, 16 at an oblique angle to the first peripheral edgeportions of the galleries.

In another aspect, the total length of fluid communication edges can beincreased further by using both internal and external edges of thebipolar plate to form fluid communication edges. It can be seen that theexemplary arrangements in FIGS. 1 to 4 and FIGS. 11 a and 11 b eachprovide fluid communication edges defined on an internal edge of theplate, i.e. an edge of the plate defined within a hole or aperturepassing through the plate 10, 111. In the arrangement of FIGS. 17 to 19,an even greater length of fluid communication edge is provided by usingboth internal and external edges of the plate.

Coolant fluid port 217 and anode fluid port 219 both define internaledges 310 of the bipolar plate 210. However, cathode fluid is deliveredby an external edge 311 where the fluid is constrained within a cathodeport 218 by an external enclosure discussed earlier.

In this type of arrangement, a flow field width (i.e. the length offirst peripheral edge portion or plate width across all channels) of 40mm has been provided with a corresponding total port length (i.e. totallength of second peripheral edge portions for all galleries) of 120 mm.This is made up of a cathode port 218 castellated region 231 of 60 mm,an anode port 219 castellated region 234 of 20 mm (circumferential) anda coolant port 217 castellated region 232 of 40 mm. Thus, the ratio offluid communication edge (total of all second peripheral edge portions)to flow field width (first peripheral edge portion) of at least 2:1 andpreferably 3:1 or more is possible in this arrangement. More generallythe ratio of fluid communication edge (second peripheral edge portion)of one gallery to the first peripheral edge portion of the gallery canbe 1.2:1 or even as high as 1.5:1 in the example of FIGS. 17-19.

In preferred arrangements, the ratio of fluid communication edges foreach of the cathode:anode:coolant is preferably of the order of50%:16%:34%. However, other ratios can be selected according to thedesign parameters of the fuel cell stack. The castellated structures 31,32, 34, 131, 132, 134 can provide any suitable aspect ratio of open toclosed to optimise flow rates versus supporting strength againstcompression of the gasket layers, but a 50%:50% aspect ratio is found tobe optimal with certain designs.

In practice, it is often found that cathode fluid flows and coolantfluid flows are the largest and/or most critical and thereforemaximizing the lengths of fluid communication edges for the cathode andcoolant galleries at the expense of reduced fluid communication edgesfor the anode galleries can be beneficial.

Another important feature of the embodiments described above is theability to feed two or three different fluids into two or more ofcoplanar anode, cathode and coolant channels 72, 73, 74 (FIG. 7) or 22,13, 14 (FIGS. 1 and 2). Fluids are delivered to a stack of plates 10 byports passing through the planes of the plates. These ports are seen inFIGS. 1 and 2 comprising anode ports 19 a, 19 b, cathode ports 18 a, 18b and coolant ports 17 a, 17 b. Thus, if the plane of the plate 10 issaid to lie in an x-y plane, the ports all extend in the z-direction butare spatially separated from one another in the x-y plane.

The galleries delivering fluids should preferably all extend across thefull width (x-direction) of the flow field of the plates, while beingseparated at their fluid communication edges with the ports 17, 18, 19.This can be achieved by providing three different levels, or planes, ofgalleries all of which occupy one common level, or plane, of thecoplanar anode, cathode and coolant channels. The expression “plane” or“level” in this context is intended to specify a finite space along thez-dimension. The anode channels 72, cathode channels 73 and coolantchannels 74 occupy a common plane, level or “z-space” referred to as thechannel plane. The anode gallery 21 a, 21 b, 121 a, 121 b, 221 occupiesa thinner plane within the channel plane, but different from a planeoccupied by the cathode gallery 15 a, 15 b, 115 a, 115 b, 215. Thecoolant gallery 16 b, 216 occupies a plane within the channel plane butdifferent from either the anode gallery plane and the cathode galleryplane.

With reference to FIG. 8, it can be seen that the cathode gallery 15 bhas an array of first fluid transfer points 301 where it meets the endsof the cathode fluid flow channels 13 at the edge of the cathode fluidflow field defined by the channels 13. This can be considered to be afirst peripheral edge portion of the gallery which extends across theflow field width. The cathode gallery 15 b also has a second peripheraledge portion defined by the castellated region 31 which forms a fluidcommunication edge 320 by which cathode fluid can flow between thecathode port 18 b and the cathode gallery 15 b.

With further reference to FIG. 5, it can be seen that the coolantgallery 16 b has an array of fluid transfer points 302 where it meetsthe ends of the coolant fluid flow channels 14 at the edge of thecoolant fluid flow field defined by the channels 14. This can beconsidered to be a first peripheral edge portion of the coolant gallery16 b which extends across the flow field width. The coolant gallery 16 balso has a second peripheral edge portion defined by the castellatedregion 32 which forms a fluid communication edge 321 by which coolantfluid can flow between the coolant port 17 b and the coolant gallery 16b.

With further reference to FIG. 4, it can be seen that the anode gallery21 b has an array of fluid transfer points 303 where it meets the endsof the coolant fluid flow channels 22 at the edge of the coolant fluidflow field defined by the channels 22. This can be considered to be afirst peripheral edge portion of the anode gallery 21 b which extendsacross the flow field width. The anode gallery 21 b also has a secondperipheral edge portion defined by the castellated region 34 which formsa fluid communication edge 322 by which anode fluid can flow between theanode port 19 b and the anode gallery 21 b.

Similar examples of the cathode fluid communication edge 320, thecoolant fluid communication edge 321 and the anode fluid communicationedge 322 are also shown in FIGS. 17 to 19. It will be seen that each ofthese communication edges occupies a slightly different z-position andforms part of the wall of the respective anode port, cathode port andcoolant port.

FIG. 20 shows an arrangement in which multiple plates 350 a, 350 b, 350c, 350 d can be formed side-by-side from a single sheet of material. Theside-by-side configuration can be used to form extra wide plates splitinto different flow field regions each served by its own respective setof cathode, anode and coolant ports (e.g. coolant ports 217 a-217 d),and its own respective set of anode, cathode and coolant galleries.Alternatively, the side-by-side configuration can be used to form plates350 a, 350 b connected by a fold line as discussed earlier, such thatadjacent plates 350 a, 350 b respectively comprise an anode plate and acathode plate which can be folded over one another to create the bipolarplate.

The embodiments shown in the figures all relate to bipolar plates inwhich an anode flow field (defined by channels 22) is provided on oneface of the plate 10 and a cathode fluid flow field (defined by channels13) is provided on another face of the pate, while a coolant fluid flowfield (defined by channels 14) is provided within the plate. Theprinciples of extending the combined lengths of second peripheral edgeportions 31, 32, 34 of at least two of the fluid galleries 15, 16, 21compared to the length of the first peripheral edge portion (bounded bythe fluid transfer points 301, 302 or 303) can also be deployed in amonopolar plate, e.g. where only a cathode flow field and a coolant flowfield is required. In such circumstances the anode flow field could beprovided by a separate plate.

Similarly, the principles of disposing at least two second peripheraledge portions 31, 32, 34 at oblique angles to the first peripheral edgeportion (bounded by the fluid transfer points 301, 302 or 303) toprovide a total length of the array of second fluid transfer points thatis at least as long as, and preferably longer than, the length of thearray of first fluid transfer points can also be deployed in a monopolarplate, e.g. where only a cathode flow field and a coolant flow field isrequired. In such circumstances the anode flow field could be providedby a separate plate.

Similarly, the principles of providing a first fluid gallery whichoccupies a first gallery plane and a second fluid gallery which occupiesa second gallery plane different from the first gallery plane, and inwhich both the first gallery plane and the second gallery plane aredisposed within a channel plane can be deployed in a monopolar platewhere the first and second fluid galleries are to supply cathode fluidand coolant fluid. In such circumstances the anode flow field could beprovided by a separate plate.

Other embodiments are intentionally within the scope of the invention asdefined by the appended claims.

1. A fluid flow plate for an electrochemical assembly, comprising: aplurality of first fluid flow channels extending across an active areaof the flow plate to define a first fluid flow field of the fluid flowplate; a plurality of second fluid flow channels extending across theactive area of the flow plate to define a second fluid flow field of thefluid flow plate; an array of first fluid transfer points disposed alongan edge of the first fluid flow field for communicating fluid into orout of the first fluid flow channels; an array of second fluid transferpoints disposed along an edge of the second fluid flow field forcommunicating fluid into or out of the second fluid flow channels; afirst fluid gallery having a first peripheral edge portion bounded bythe array of first fluid transfer points and having a second peripheraledge portion forming a first fluid communication edge of the fluid flowplate, a second fluid gallery having a first peripheral edge portionbounded by the array of second fluid transfer points and having a secondperipheral edge portion forming a second fluid communication edge of thefluid flow plate, wherein the first fluid gallery and the second fluidgallery are shaped such that the combined lengths of the secondperipheral edge portions are longer than the first peripheral edgeportion of the second fluid gallery or the first fluid gallery.
 2. Thefluid flow plate of claim 1 in which the fluid communication edges ofthe fluid flow plate comprise internal edges of the flow plate.
 3. Thefluid flow plate of claim 1 in which the fluid communication edges ofthe fluid flow plate comprise both internal and external edges of theflow plate.
 4. The fluid flow plate of claim 2 in which the internaledges of the flow plate form at least part of at least one port passingthrough the flow plate.
 5. The fluid flow plate of claim 1 in which thecommunication edges each comprise a castellated structure.
 6. The fluidflow plate of claim 1 in which the second peripheral edge portion of thesecond fluid gallery comprises at least one edge disposed at an obliqueangle to the first peripheral edge portion of the second fluid gallery.7. The fluid flow plate of claim 1 in which the second peripheral edgeportion of the first fluid gallery comprises at least one edge disposedat an oblique angle to the first peripheral edge portion of the firstfluid gallery.
 8. The fluid flow plate of claim 6 in which at least oneof the first fluid gallery and the second fluid gallery has a portionwith a generally triangular configuration, the first peripheral edgeportion forming at least part of a base of the triangular configurationand the second peripheral edge portion forming a side of the triangularconfiguration.
 9. The fluid flow plate of claim 1 in which the firstfluid gallery and the second fluid gallery are at least partiallyoverlapping one another.
 10. The fluid flow plate of claim 9 in whichthe first peripheral edge portion of the first fluid gallery and thefirst peripheral edge portion of the second fluid gallery are superposedon one another.
 11. The fluid flow plate of claim 1 in which the secondfluid gallery is shaped such that the second peripheral edge portion islonger than the first peripheral edge portion.
 12. The fluid flow plateof claim 11 in which the second fluid gallery is shaped such that thesecond peripheral edge portion is at least 1.2 times longer, orpreferably at least 1.5 times longer, than the first peripheral edgeportion.
 13. The fluid flow plate of claim 1 further including: aplurality of third fluid flow channels extending across the active areaof the fluid flow plate to define a third fluid flow field of the fluidflow plate; an array of third fluid transfer points disposed along anedge of the third fluid flow field for communicating fluid into or outof the third fluid flow channels; a third fluid gallery having a firstperipheral edge portion bounded by the array of third fluid transferpoints and having a second peripheral edge portion forming a third fluidcommunication edge of the fluid flow plate, wherein the third fluidgallery is shaped such that the length of the second peripheral edgeportion of the third fluid gallery is at least as long as the firstperipheral edge portion of the third fluid gallery.
 14. The fluid flowplate of claim 13 in which the first fluid gallery, the second fluidgallery and the third fluid gallery are all shaped such that thecombined length of the second peripheral edge portions thereof is atleast two times longer, or preferably at least three times longer, thanthe first peripheral edge portion of the first fluid gallery or thesecond fluid gallery or the third fluid gallery.
 15. (canceled)
 16. Thefluid flow plate of claim 3 in which the internal edges of the flowplate form at least part of at least one port passing through the flowplate.
 17. The fluid flow plate of claim 7 in which at least one of thefirst fluid gallery and the second fluid gallery has a portion with agenerally triangular configuration, the first peripheral edge portionforming at least part of a base of the triangular configuration and thesecond peripheral edge portion forming a side of the triangularconfiguration.